Piezo-electric device and method of producing the same



game 29 m l A. MCL. NCOLSN FIEZG ELECTRIC DEVICE AND METHOD OF PRODUCING THE SAME Original Filed April 1l. 1921 .nii

LEXAR-IDEE CL. NICELLSOBL' DF ELECTRIC COMPANY?, NEW YORK.

HILLSDMAE, NEW dERSEY, .ASSIGNR T0 WESTERN XNCDRPORATED, Gl? NEW' YORK, N. Y., A. CRPRATIN OF PEZOJELECTRIC DEVICE .ill METHOD 0F PRGDUCING THE SAME.

.fzi'ginal application filed ipx-il l1, 1921, Serial No. 430.396. Divided and this application led July l?.

This invention relates to piezo-electric devices and methods of producing the saine.

rlhe invention aiins to provide a sensitive, cliicient, simple and durable piezo-electric crystal device for translating clcctri al variations into mechanical vibrations, and vice versa, and, therefore. capable of serving as a telephone transmitting or receiving device for instance.

Other objects of the invention will be upparent from the detailed description hereinat'tcr ot' the accompanying drawings.

(lt the inany mineral and organic crystals investigated by H. and l). Curie andothers, (see l?. llockels, llr'inlie'hnanns l-landb. d. Phys., lll). IV, p. 7 the crystal of Rochelle salt (sodium potassium tartratc. Nali'l -liC/llllQ) was found to have the. largest zii-electric constant. approximately il? electrostatic unitsper kg.- Apparently no other crystalihas yet been found to approach the piezolectric activity of Rochelle ysalt. particularly it the crystal is carefully chosen and specially prepared. It has been found that- Rochelle salt. is susceptible of greatly increased piezo-electric activity. An absolute electric charge ot 200 electrostatic units per kg. pressure has been obtained, resulting in potentials high as 500 volts and alternating currents as high as 2() microainperes. Acoustic tones troni a crystal may be heard at a distance of several hundred feet.. lricily, the increased etlicicncy is 'brought about by the following: conditions:

`= lelection oi particular habit oi ,g'roWth.

lesiccation.

El. Development posite polar si xuctnre.

4. .pplic tion ot static compressioln 5. ilse ot electric poles normal to each other. Y',

6.' Application olf torque.

vThese conditions will be considered in detail in connection with the drawings.

Fig. l is a sectional elevation showing a vessel containing two crystals of a type suit able for use in this invention, Growing in accordance with the method described below;

Fig. 2a is a plan of the apparatus and crystals shown in Fig. l;

Fig. 3 is a perspective view of. a crystal grown in the ienne; indicated in Figs. i and 3 ywhich indicate thc ol' the crystal into a conisemi no. 575,473.

Fig. 7 is a perspective View of the device shown in l"i (i with the addition of acylindrical soundalirectinpr member.

Referring.;r especially to Figs. 3 and 4, general appearance ot crystals grown in accordance with the method described below, the crystal surface may beclassiiied into twosy tenis of surfaces or zones which are noriiiai to each other. ()1ie"fs \'stem of Zones is parallel with the principal or crystallographic axis c and, therefore engirdles the crytal. The other system Aotl zones comprises the .two basal planes parallel with the a and axes. ln the method described herein, the crystals are grown with the c and b axes in a horizontal position. as is indicated in Fig. 1. This 'growth forms a particular habit, becoming dominant along the c and ZJ axes, while development along the a axis upwards, is partially suppressed on account ot the supersaturation and consequent gradation in density of the bauer.

`The crystals are grown from perfect nuclei possessing deiinite torni and having,r a, b, and c axes corresponding to the a, b, and c axes7 respectively, of the crystals shown in Fig. 3. In obtaining seed crystals, generally from a previous cropping, those seeds are selected in which growth along the b axis is fully developed which happens when the seed nucleus grows with its c and o axes horizontal). These seeds are square, or nearly so,

c signifying thatJ the growth along the b axis li uor.

i iFgs. l and 2 the vessel. 13 contains gli .ln growing a crystal in the manner in dicated in Figs. l and 2, a seedling.,r 2l, to,

the bottom of which a small quantity o f wax or like adhesive has been applied, is placed horizontally on top of the support l() with the c axis of the seedling parallelv to the surface ot the support, the seedling and the mother liquor being between a temperature o'E 38 and 35 C., and the concentration of the mother `liquor being such that the density of the solution at 50C C. would be about 1.33. The apparatus is then allowed to cool from between 38o and 350 C. to room ten1peraturc,for instance to about 200 C. On thus cooling rapidly the seed crys= tal will increase in size from a few grams weight to 5U or 50i) grams,4 according' to the volume and densityT of liquor used. Growth occurs.principally during the lirst l() hours. although it may be continued sev-v eral days during the condition of supersaturation if the crystal is allowed to remain in the mother liquor. An average size of crystal weighs 100 grams and its l) and c axial lengths cach approximate mm., the proportions of the crystal beingr about those indicated in Fig. 3. The coolingr of' the apparatus to room temperature ordinarilyrequircs from about five to ten hours, the time being largely dependent on the volume of mother liquor used. is 'fairly rapid at first and tapers ofl.l as the temperature of the apparatus approaches the room temperature. rEhe crystal usually grows to the desired size, for instance to such a size that it weighs about l0() grams, duringl this period of from tire to ten hours, and may be taken -fr m the mother liquor when it has attained such size.. lt appears probable that this .rapid growth. due to the rapid cooling,r of the mother liquor causes the crystal to develop internal stresses producingY strain regions symmetrical with the principal axis. composite structure closely related to the surface zones referred to above and to the' electric poles to be developed in a manner which will now be set forth. At each end of the seed nucleus and along its c axis there appears a pyramid, the base of which forms a polar terminal. The pyramids are not always very pronounced in the seed nucleus, but are more evident in the grown crystal utter the latterl hasbeen Clesiccated as described hereinafter. The pyramids in the crystal are indicated at 23 in Fig. 4. They consist of Stratcat-ons parallel tothe The rate ot' coolingrv rl`he crystal thus acquires a' Z axis and normal to the c axis and to the remainder ot the crystal structure, the stratification of w hich ordinarily is parallel with the c axis. The electrical performance o't' the crystal suggests that the crystal molecules throughout the pyramidal regions during growth, are subject to forces which turn them, in planes containing the principal axis, through a right angle. This is indicated by the fact that the crystal, after subsequent treatment tending to render more pronounced these pyramidal terminations, develops its electrical poles (plus and minus corresponding with the conventional analogous and antilogous poles) in accordance with the two systems of zones referred to above. The polesl are accordingly orthog onal, that is, at right angles to each other. This signifies that the bases of the pyramids. which 'occupy almost the entire area of the. basal planes of the crystal, are electrically plus when the rest of the crystal structure is minus and Avice versa. The effeet becomes very pronounced when the crystal is subsequently desiccated in a manner which will now be described.

The desiccatingr treatment comprises submerging the crystal in 95%. alcohol for about twentydour hours, and 100% alcohol for about six'hours, removing the crystal from -for drying the-crystal is preferably a pressure o about one or two millimeters of mers cury and the crystal is preferably subjected to the low pressure before it has heen heated, and for a period of about 24 hours. The heatingr is performed in an oven. at about "IO C. for a period of several days, or at a slight-ly higher temperature for a somewhat shorter period.

This treatmfmi` of the crystal is largely for removing waters of inclusion. The crystal prepared in the manner decribed above will no longer be clear as when it was taken from the. mother liquor, but will be cloudy or opalescent. the surface of the crystal showing irregular white spots and the crystal exhibiting the pronounced houcglassi` marking indicated at 23 in Fig. 4. The raw crystal as taken from the mother liquor possesses a large numberof local electric poles which are variable in their piezoelectric etl'ect. The desiccated crystal .is much stronger in efect and its electric poles are readily found in the case of the composite crystal to reside as described on the crystal, surfaces with corresponding signs, respectirely` in the zones parallel to the o axis and the zones normal. to the c axis.

nos

ln order' to prepare the crystal for piezoelectric use, a tint'oil electrode is pressed around the girdle pole'o. the crystal and tintoil electrodes are pressed on the basal planes, that is, the c axis. The tinfoil is waxed on the side to be applied to the crystal, to make it adhere closely to the crystal. Beeswax has been found'suitable for this purpose.

`Referring; to Fig. 5 (described in detail later) it Yill be noted that bota basal'planes 27' and 29 of the crystal 15 areslightly vconcave in the central or polar regions. This featureis obtainedvin a crystal either by tiling the basal planes of the crystal or by growing the crystal in a particular manner described hereinafter. The object ot' this featurev is to render salient the ends of the basal planes ot the crystal. [is pointed out in the article on The piezo-electric etl'ect in the composite Rochelle salticrystal, by A. M. Nicolson, in the proceedings of the A. I. E. E., November, 1919, these ends of the basal planes are found to be mechanically sensitive regions. of the crystal, just as were the ends of the basal planes of the corresponding crystal deseribedin the U. S.

`patent application of Nicolson. Serial a 295,967, tiled May 9, 1919, entitled Piezoelectric transmitter. Rendering the diagonal corners of the crystal salient is for the purpose et' insuring that when the crystal is mounted between compressor' plates, such as 53 and 55 in the general manner indicated in Fig. 5, the pressure brought to bear on the crystal will. be effective on these corners, so that stresses transmitted from the plates to the crystal will be elliciently applied to the crystal. Obriously. this purpose may also be realized by leaving the basal planes of the crystal flat and makingr the compressor plates concave toward the crystal.

For the purpose of obtaining an ellicient piezo-electric action at least tivo or' these .four diagonal corners at one crystallograpic pole of the crystal should be perfect and flawless, apart fronr the composite structure referred to above. l

As pointed out in the Nicolson article referred lo above in the il.. l. E. ll. proceedings, analysis ot' the direction of applied stresses to the sensitive regions described hais shownthat with crystals having the composite structure referred to above, a given torce produces the greatest piezoelectric etlect when the force is applied in such a way as to twist the crystal about 'its principal axis, and conversely, an applied electrical torce produces the maximum mechaiical response in the 'form of twisting motion, and, therefore, it is apparent that Whether electrical or mechanical results are to be produced from the crystal the torsional efiect should be utilized as far as possible, for instance as the graphophone the planes perpendicular tol ltic-'rod is preferably riveted to one of transmitter described in the Nicolson application Serial No. 295,967, referred to above, utilized the torsional effect ina piezo-electric crystal.

A crystalgrown. in the manner described above, has a reentrant bottom face, --as shown at in Fig. 3, and due to the prevention of upward growth, has but little thickness in the plane through the A and t) axes. Due to-this reentrant face and Ithis thinness, the crystal is easily deforn'xable by stresses torsional with respect tothe principal axis oi the crystal. lt appears that the piezo-electric eilect of the crystal is thereby greatly increased. The area ot the basal planes or end poles 27 and '29, should not be too small, and, therefore, the crystal as a Whole should not be too thin. 'l`herct`ore, the cylindrical support 19 should notbe too nearly fiat.

A piezo-electric crystal, such as lo' for instance, mounted as` shown in Fig. 5, lie-- tween tivo electrically conducting compressor plates such as 53 and 55 with its basal planes electrically connected together to forni a pole ot' one sign, and mal to the basal planes electrically connected to forni a pole of opposite sign, may be used to translate mechanical vibrations into electrical vibrations, or vice versa, the plates readily conveying' vjarsand vibrations to the crystal. rThe members 53 and 55 are preferably ot' aluminum. With a crystal having a channel-shaped face parallel to the principal axis, a single tie-rod 59 lying;l within the channelY formed by the concave tace, may be used to hold the crystal and the plates 53 and in thc desired relation. An insulatingr layer of rubber tape 66 may be wound upon this tic-rod. The rod may serve to electrically connect plates 5S and 55. The the plates, as shown at (S0. The other plate may be\slipped on thc tic-rod and held against the crystal with the desircd degree of pressure by means 'ot' a nut 6;). threaded on the tie-rod. (lr the latter plate may itselic be `thrczu'led on the tic-rod, in which case thc nut 6i. is not essential but may serve to lock thc plate in the position in which it exerts` the desired deirrcc of pressure on the crystal. A spring' washer 64 is preferably interpascd l'ictwccn thc plaie and thc nut. The degree 0f static pressure exerted upon the crystal by the plates preferably corresponds to an absolute force of about lo' kf.. since, as ex'- plained in the Nicolson application Serial No. 295,967 referred to above and in the Nicolson article in thc/A. I. ll. E. proceedings referred to above, the composite crystal is then most sensitive to variations of pressures applied so as to bear on the salient ends of the basal planes simultaneously. This static pressure will ordinarily be sulcient to prevent slippage betWQQll the plates and the its surfaces norlll) crystal when the crystal is being subjected to vibrations torsional with respect to its principal axis. However, a small quantity of 'dental' cenicut or melted Rochelle salt or f may be utilized for connecting one pole of the receiving or transmitting device to the circuits in which the device is to be used. To electrically connect thegirdle electrode of the crystal with the circuits'in which the transmitting or receiving device is to be used, several layers of tin foil are Wrapped around the girdle pole, as shown at 63, and several turnsl of Wire are Wrapped around the tin foil 68, several layers or Wrappings of tin foil 67 and a layer of rubber tape 65) being then applied. The tie-rod 59 passes between the crystal and all of these Wrappings. The Wire 65 is preferably brought out from the device through an insulating bushing 71 in one of the plates 53 or 55.

As indicated above, the' metal plates in Fig. 5 readily convey jars and vibrations to the crystal. The crystal and its niounting, as shown in Fig. 5, therefore, constitute an elicient generator or transmitter for converting the energy of sound 'waves into the energy of similar electrical waves. lfl this crystal transmitter be laid on a large sheet of paper and receivers be applied to the electrodes, sound produced by rubbing on the paper, or by the ticking of a watch, will be transmitted to the plates by the paper and can be heard in the receivers.- Care should be taken that the tie-redo() does not pro trule below plate 55, since when the transmitter plate 55 rests on a vibrating surface the vibrations are most efficiently transmitted to the crystal if the portions of the plate adjacent its perimeter are in intimate con tact with the vibrating surface.

Th device of Fig. 5 may also be used. as a receiver, since the application of electromotive force waves to its poles will produce corres onding mechanical vibrations of the two p ates- 53 and 55 in opposite'rotaticnal senses.

As indicated above, the crystal operates most efficiently as a v.translator of electrical into mechanical energy, or vice versa, when the vibrations to which it is subjected are, as far as ossible, torsional with respect to the c axis of the crystal. Thus, it has been found that the eil'iciency of. the device shown 1p, 5 may be materially increased the periphery of disc 55 and clamped thereto by means of the clamp 77. The cylinder so formed by the paper is then twisted about its and clamped to the periphery of the disc 53 by means of the clamp 79. Spiral corrugations til'are thus formed in the paper diaphragm and 'when the device is used as a transmitter or electrical generator, lneclianical stresses normal to the surface of the cylinder tend to vary the length of the cylinder. This tendency to change in length results in a further twisting or in an untwisting of the diaphragm., but as a result of the clamping of the diaphragm to plates 53 and the twisting or untwistin of the dia phragm results in the rotation of plate '53 in one sense, and rotation of plate 55 in an opposite sense. Thus reaction to the twisting or untvvistingr is equally divided between and balanced by the upper and lower plates: Consequently impinging Waves are trans' lated entirely into torsional stresses on the' crystal which has no tendency to rotate as a unit about its c axis. lNhen the device is used as a receiver, torsional vibrations clec rically produced in the crystal twist the diaphragm, thereby etliciently setting up correspending air vibrations. It is to be noted that as a result of the normal twisted conditionot the diaphragm 75 torsional effects produced therein by an electrical charging of thecrystal poles will have a tendency to expand or contract the. crystal in the direction of its principal axis.

As stated in the Nicolson article in the proceedings of the A. I. E. E., mentioned above, the crystal may be considered as a leaky condenser having a shunt resistance in excess of 100 megchms, and a capacity varying with the size oi the crystal and usually of the order of 10" F. The imppdance of the crystal at acoustic frequencies varies i from 100,000 to 800,000 ohms. If the crystal receiver is used Wit-l1 a Vmicrophone transmitter, the supply potential for the crystal should preferably be stepped up to the ctylsl tal by means of a transformer. 'The motionl impedance of the crystal may be found in the same manner as the motional impedance of an ordinary telephone receiver.

It has been found vthat the eiiiciency of the device shown in Fig. 6, especially when the device is being used to transmit speech, is increased by the use of a supplementary cylindrical corrugated aper diaphragm parallel to and somew iat longer than the diaphragm 75, as shownx in Fig. 7 The`sup lementary diaphragm may consist of the corrugated cardboard commonly used for lllO use

packing articles to be shipped, and may be strapped around the device shown in Fig. 6 by means of a rubber band 8i', or the like, to form the device shown in Fig. T.' One end Si) of the supplementary cylinder is preferably extended beyond the cylinder a distance equal to about half the axial length of cylinder 75. ri"he operator talks into this end of the supplementary cylinder, the sound passing down he corrugations oi the supplcmentary cylinder around the compressor plaie nearestJ this end. The other end of the supplementary'cylinder preferably ex tends but a short distance beyond the cor responding end of the cylinder 75.

The expressions cylindrical concave and Lcylindrical reentrant and the like, as used herein to describe crystal faces, are intended to apply to prismatic or other cylindrical hollowed out surfaces having a right section of a general arch or C shape, and the arch or C simulated ma be asnearly a closed ligure as desired., The expressionn cylin- 1li-ical convex is used in a similarly broad sense. Where a crystal has a cylindrical upivardly convex lower face of Which-the right section is nearly a closed ligure, the crystal may be removed from its mould by sliding,r the crystal parallelto its c axis, the mould having no end walls. In some cases a reentrant face of a crystal may be such that its right section presents a plurality of sharply reentrant cusps superposed on theygeneral line oi reentrancy, for the purpose oli malring the crystal the more readily deformable by stresses torsional with respect to the c axis. Such a crystal face would, of course, be obtained by hai-'ing a complementary face on the nioul or support used in growing the crystal.

This application is a division of my application, Serial No.

460,396, piezo electric devices and methods of producingl the same, which was issued as Patent No. 15.138,965, December i9, i922, and which was continuation of .my application Serial No. 226,3e3, filed April 2, i918, method of mal:n ing piezo-electrical crystals, (patent No. 1,414,370, May 2, l92;?} Serial N 227,802, filed April 10, 19l8, piezophony (Patent No. 1,495,429, May 27, 1924); and Serial No. 295,967, liled May Q, 1919, piezo-electric transmitter, as regards common subject matter.

The crystal and the method of making it disclosed in this application are claimed in application Serial No. 460,39. il' y application Serial No. 740546, liled September 3G, 1924, entitled, Cement composition and method of preparation, claims a cement made from sodium potassium tartrate, and. the rocess of making the cement.

l at is claimed is:

l. A piezo-electric crystal and a mount: ing therefor, said crystal having a channel shaped face, said mounting comprising two plates and a tie member and said tie eri-l tendingV between said plates and lyingr at least partly Within the channel forme y, by said face. y

2. A piezoelectric crystal and a mounting therefor, said crystal having a channel shaped face, said mounting comprising two parallel and said tie extending between said discsy and lying in the channel formed by said face.

3. Two compressor plates, a. piezo-electric crystal therebetween, and a single tierod betyveen said plateseilor maintaining said plates in compressing relation with re speci: to: said crystal.

el, ,llfwo compressor. members, triccrrystal therebetween, and a tie member extending from the center of one of seid compressor members the center oi" the other of said compressor members.

5. A piezo-electric crystal and a, mounting:T lberefor said crystal having a channel shaped face, said mounting comprising an electrically conducting plate against one a piezoelecpole of said crystal, an electrically condi1ctin c' plate against another pole of said crystal. and an electrical conductor extending' between and electrically connecting said plates and lying in the charmed formed by said' i'ace. t

(LA pier/oelectric crystal and a mountn ingf there-for, said rcrystal having a channel shaped' Jlace, said mounting comprisingr an elecirically conducting plate against one polo,` ol' said. crystal and an electrically conduciiing plate against another pole oi.g said crysial, an electrically conducting tie niemloer extending bet-Ween said plates and lyingn in the channel formed by said face, said tie member being insulated from said face, and an electrical conductor substantially surrounding said crystal in a planesubstantially perpendicular to said tie member.

Y. A device for translating electrical err orgy into mechanical energy and vice versa, said device comprising two parallel come prcssor discs, a piezoelectric cry'sal there between, and af cylindrical diaphragm eX- tcnding from the 'periphery of one of said discs to the periphery of the other of Said discs. 8. A device for translating mechanical energy into electrical energy and vice versa, said device comprising a piezo-electric crys- Ytah'a mounting` for said crystal, and 'a cylindrical diaphragm, said crystal having a channel shaped face, said mounting1 comprising two compressor discs and a tie member, said tie member extending between said discs and lying,r in the channel formed by said face, and said diaphragm extending from the periphery of one of said discs to the periphery of the other ci said discs.

compressor discs and a tieV member,

lill

las

9. A teiephone receiyer. or transmitter comprising two parallel'coinpressor discs, a piezo-electric crystal therebetween having one pole inv Contact with one ot' said discs and having another pole in contact with the other of said discs, and a cylindricalyspirally corrugated diaphragm extending between the perimeters et said discs.

10. A telephone receiver or 'transmitter' comprisingtwo parallel compressor discs, a piezo-electric crystal tl'ierebet-ween having one pole in Contact with one of said discs and another pole in contact with the other of said discs, a tie-rod connecting said. discs, and a twisted cylindrical diaphragm extending 'between the perimeters of said discs.

l1. The method of making a telephone receiver or transmitter which comprises mounting a piezo-electrical crystal between two parallel discs, fastening a flexible sheet to one of said discs around the periphery ot said disc, to Aform a cylinder having said disc as a base, tensioning said cylinder in the direction of the axis and twisting said cylinder about its axis, and fastening said cylinder to said other disc around the perilihery of said other disc.

12. A device for translating electrical energy into mechanical energy' and vice versa, said device comprising two parallel compressor discs, a piezo-electric crystal therebetween, a cylindrical spirally corrugated diaphragm extending from the periphery ot' one of said discs to the periphery of the other of said discs, and a cylindrical member surrounding said diaphragm and.

extending beyond one end of said dia phragm and having channels for directing sound waves with respect to said corrugated diaphragm.

13. Two plates, a piezoelectric crystalline body therebetween, and means for maintainingvsaid plates in compressing relation with respect to said body, said means comprising a substantially rigid tie-rod cxtending from one of said plates'to the olhcr.

14. telephone receiver or transmitter comprising ltwo parallel compressor plates, means therebetween capable. of reversibly converting variations of mechanical pres sure into electrical variations, and a yielding diaphragm stretched between said plates.

'15. A device for translating electrical energyr into mechanical energy and vice versa, said device comprising two parallel compressor discs, a piezo-electric crystal body therebetween, a diaphragm extending from the periphery ot' one ot said discs to the periphery of the other of said discs, and means substantially surrounding said diaphragm for directing energy waves with respect to said diaphragm.

1G. A telephone instrument comprising two parallel compressor plates, a. piezo elec tric crystalline body therebetween, and a yielding diaphragm stretched from the per imeter ot" one of said plates to the perimeter of the other of said plates.

17. A telephone instrument comprising two parallel compressor discs, a piezo-electric crystalline body therebetween, a. cylindrical, spirally corrugated diaphragm extending trom the periphery of one ot' said discs to the periphery oi the other oi' said discs, and means substantially surrounding said diaphragm tor directing sound waves with respect to said diaphragm.

18. A device for translating one form of energy into another, one of said forms being electrical and the other mechanical, said device comprising a. piezo-electric crystal line element, a yielding diaphragm element, and substantially incompressible means mechanically connecting the crystalline body and the diaphragm wherebyY mechanical deformations of one of said elements may cause corresponding` vibrations of the other ot said elements.

19. In combination a piezo-electric crystalline body, a. diaiihragm, and means for so associating said diaphragm with said body that said body is capable ot' causing motion ot' said diaphragm in the direction of the axis ot' said (.liapln'agm inresponse to twisting of said body.

20. 1n combination a crystalline sodium potassium tartrate body having a principal axis, a diaphragm, and means for so asso- `ciating said Adiaphragm with said body that vibratory twisting ot' said body with respect 'to said axis is capable ot producing vibrations oi said diaphragm in the direction of the axis of said diaphragm.

21. The combination with a diaphragm for radiating sound, of i'ncans for twisting said diaphragm.

22. The combination with a diaphragm for radiating sound, of clectro-responsve means for setting up vibraory twisting of said diaphragm.

E23. The combination with a diaphragm for radiating sound, of piezo-electric means for setting up viliratory twisting ot' said daphragm.

24:.` In combination, a piezo-electric body, a diaphragm so associated with said body that said body is capable of vibratino' said diaphragm in response to twisting ot said body, and means for causing twisting of said body.

Q5. In combination, a piezo-electric body, and a diaphragm so associated 'with said body that said body is capable of vibrating said diaphragm in response to longitudinal vibrations of said body and in response to twisting vibrations of said body, and means for causing both of said kinds of vibrations of said body.

2S. ln combination, a piezoseleciric body, a diaphragm so associated with said body that said cody is capable oi vibrating said diaphragm in response to longitudinal vibrations ol' said body and in response to twisting 'vibrations oi' said body, and. means for subjecting said body static longitudinal compression.

2?. A piezo-electric sirnctnre, diaphragm ineens for operacion oy twisting of said structure, and means so associacing said diaphrarn means with said structure that the reaction-of said diaphragm ineens upon seid structure is a balanced reaciion.

28. A. piezo-electric structure, diaphragm means for operation oy twisting of said sirnctnre, and ineens so associating said diapinagrn means with said structure thai the reacion of said diaphragm means upon said sirncure has no tendency to move said structure as a Whole.

29. A piezoelectric sirncnre, a dlapliragn structure, and means associating said structures for operation o' one by twisting of the einer, said ineens insuring that the raction of each strncl-ure upon the other is a balanced reaction.

80. in combination, means comprising a piezo-electric body, for translating electrical energy `into torsional elastic vibrations oi said body, a sound radiating diaphragm, andineans, comprising said diaphragm, substantially inclosing said first mentioned means.

1 3l. In combination, a sound radiating dicpliragm means comprising; a closedenvelope, a piezo-electric body for vibrating said diaphragm means in response co torsional elastic vibrations of said body, and means for producing said torsional vibrations.

A. device, comprising a piezo-electric body, for translating electrical oneri-ry into elastic torsional vibrations of said body and Vice versa, said device comprising means associated with scid body for directing sound waves witlrrespect; Ato said body. i S3. A. piezo-electric `sirucianre having an axis, a diaphragm means for snbieccing said cryssal to pressure at each enel of .said asis, and means connected to said srnclzare, ar, each end of seid axis, fos transmiting, be tween said diaphragm and said structure, forces torsional wili respect io said axis.

Si. A. piezoelectric .structure having an axis, a diaphragm, means for subjecting said crysal to pressure ai; one end o said exis,

and means connected to said structure, at one end of seid axis, for transmitting between said diaphragm and said structure, forces torsional with respect to said axis.

35. A piezoelectric device comprising an active crystal and comprising means for subjecting said crystal to pressure along an axis and to doable torsional elec at the ends of said axis. i

36. A piezo-electric device according io claim 35, which comprises a sound receiving and ransmiiiting surface and a pair of meinbers connected dirccly to the receiving and transn'iitting surface, and in which the double torsional eilecl; is appliedv to the crystal by means ci said members.

3T. A piezoclcciric device, comprising an active crystal, electrical contacts upon said crystal, ineens for subjecting said cr Stal to pressure along an axis, and means or sub "Ill jecting said crystal to torsion at opposite ends of said axis.

3&3. 'A piezo-electric device, comprising an active crystal, electrical contacts upon said cryslal, means for subjecting said crystal to pressure along an axis, a torsional member clamped to one of the. basal planes of said crystal by said pressure means, and means for exerting an opposibe torsional eiiect at the other basal plane of said crystal.

39. The method of operating a Sound re'- producer which comprises subjecting said reproducer to twisting vibrations similar in form to the sound Waves to oe reproduced. ci), A. inbular sound radiator, s source of electrical waves all similar in forni to sound' waves, and means responsive to said electricel waves for subjecting said radiator to torsion varying in accordance with said. electrical Waves.,

el. The combination willi a cylindrical diaphragm for radiatingsonnd, of means Afor t risting said diapliragm.

cl2. The comlonaion with a cylindrical diaphragm for radiating sound, of electroresponsive means for setting up vibratory twisting of said diaphragm.

43; fi piezoelecitric structure and a diaphragm nssociaied hercwitii for iransmilu ting elastic'vibrations between said struclos tere and s snrroundingmedinm capable of propagaing said elasic yibrabions.

ln wit-ness whereof, Si hereunto subscribe my naine, liliis 30tlg day of Ernie, H1922.

naissances Mss.. lnrcorison. 

